Sounds like a vs test. You could also make up a version of Fight! Rules for it if you want to make it more than one roll.

I think we actually did something like this in an old campaign where two PCs were playing spirit binders and were somewhat antagonistic toward each other from time to time due to opposing motives. And yeah, we handled it with a VS test. Keep it simple!

In our current game, two spirit binders seem set to clash head-to-head in the near future. Assuming that they're both bound to a domain, what's the best way to handle it when they're fighting over spirits? How should we resolve it when one says, "I want to bind the storm to harm my enemy" and the other says "I bind the storm so it won't harm me then!" or "No, *I* bind the storm to harm *my* enemy"?

A clash of spirit binders